1. Field of the Invention
The following invention relates to a clot filter and more specifically to a convertible vena cava blood clot filter.
2. Description of the Related Art
Vena cava blood clot filters are generally placed in the inferior vena cava, introduced either through the femoral or jugular vein. These filters trap blood clots that have arisen from the peripheral veins and that travel through the vena cava. By trapping the blood clots, the filter prevents the clots from lodging in the pulmonary bed, which can lead to a condition known as pulmonary embolus.
Pulmonary embolus (PE) has long been recognized as a major health care concern. Untreated PE is associated with a high mortality rate, widely held to be approximately 30%, although the exact rate is unknown. Symptomatic PE, however, represents only one manifestation of a more protean disorder, venous thromboembolic disease (VTD), which includes both deep venous thrombosis (DVT) and PE. Understanding of the interrelationship of these disorders has increased in recent years, as has the extent to which VTD contributes to patient mortality.
The current standard of care of VTD is anticoagulation for a minimum period of six months. If patients are properly treated with anticoagulation, the impact of VTD upon patient health is minimized. However, anticoagulant therapy carries the risk of bleeding complications. In patients with VTD or PE that 1) are at high risk of developing a bleeding complication, 2) have a contraindication to anticoagulant therapy, 3) had a failure of response to anticoagulant therapy (i.e. further episodes of PE), or 4) developed a bleeding complication because of anticoagulant therapy, vena cava blood clot filters play an important role in the management of VTD.
Vena cava clot filters can be categorized into two device families: permanently implanted devices and temporary devices. Permanently implanted devices are implanted for patients that require a filter for more than fourteen days. Fourteen days roughly approximates the time before which the points where the filter contact with the caval wall becomes covered by endothelial cells which thicken to eventually attach the filter permanently to the cava wall. If an attempt is made to remove the filter after this time point, severe damage may occur resulting in laceration or rupture of the vena cava, or at the very least, a focal disruption of the endothelial lining which may predispose to caval stenosis, thrombosis (clot formation) or occlusion.
Since the permanent blood clot filters are left in the body for the lifetime of the patient, the patient undergoes several risks that continue throughout the person""s lifetime. The reported long-term sequela of some of the permanent devices include thrombotic occlusion of the vena cava, filter migration, filter fragmentation and filter embolization.
These problems can occur because the blood clot filter is directly in the blood stream and continually filtering the blood clots throughout the lifetime of the patient. Thrombotic occlusion and filter embolization can occur when a gradual buildup of blood clots forms in or around the filter due to the continuous filtering. Filter migration and filter fragmentation can occur because of the constant impact between the blood filter and the flowing blood can move the filter or break the structure of the filter.
Temporary blood clot filters do not share those long-term risks because they are removed from the patient""s body. However, the situations in which temporary blood clot filters are used are limited. The patient must recover to the point that the risk from PE is reduced to an acceptable level prior to the 14-day limit or to a time point at which the patient may be safely anticoagulated. Otherwise, a permanently implanted blood clot filter must be used to avoid damage to the caval wall that may result if attempt is made in removal after 14-days.
Temporary blood clot filters fall into two categories. One group utilizes a permanently attached tethering catheter for retrieval, whereas the other requires the use of a retrieval device for removal. In addition to the limited amount of time that it can remain in the vena cava, the catheter-based design has the draw back of infectious complications at the entry site. Other temporary designs allow a filter to be placed and later retrieved using a device.
When a patient""s need for a blood clot filter is known to be temporary, but longer than the 14-day period, the patient""s only recourse is to receive a permanent blood clot filter. An example of a temporary need resulting in placement of a permanent vena cava blood clot filter is a patient who need needs protection from PE in the perioperative period or a woman with DVT during pregnancy. These patients will receive a permanent filter and be unnecessarily subjected to the lifelong risks associated with permanent blood clot filters.
Accordingly, it is the object of the present invention to disclose an implanted device that provides effective caval filtration for any length of time. However, if and when it is determined that the risk from the implanted device disrupting laminar blood flow exceeds the risk of further PE, the filter can be removed from the blood stream to eliminate the associated risks of having a permanent filter within the bloodstream. This can be done at any time without regard to the amount of time that the filter has been implanted and without causing damage to the caval wall. Another object of the present invention is to provide such a filter that allows trapping (capturing) of blood clots of sizes that result in a clinically significant PE that poses an unacceptably high risk of patient morbidity and mortality. The trapped clots in the filter are then dissolved by the bodies own intrinsic fibrinolytic system, without causing pulmonary function compromise. Still a further object of the present invention is to provide such a filter that is relatively simple in design and is relatively inexpensive to manufacture.
The present invention provides a blood clot filter and a method for its use. The blood clot filter comprises an expandable filter shaped in the form of a cylinder. The filter is composed of high memory wire and the wire is formed into a band of zigzag bends.
In its pre-deployment form, both ends of the filter are collapsed to form a slender wire construct. After deployment, one end of the cylinder is held together by a suitable restraining means such as a Teflon ring with a diameter of approximately 3 mm. The other end of the cylinder is expanded and has a sufficiently large diameter to contact the walls of the inferior vena cava with sufficient force to hold the filter in place against the inferior vena cava. Additional means are used to attach that end of the filter to the walls of the vena cava.
When it is desirable to stop filtering, the Teflon ring holding the narrower end of the filter is broken thereby releasing the end of the filter. Once released, the narrow end of the filter will expand until the entire filter lines the walls of the vena cava. The filter will no longer filter the blood nor will it be directly in the blood stream.